Question

Is 2-Naphthol polar or nonpolar?

Is Phenol polar or nonpolar?

2-Naphthol looks like it may be polar because of the hydrogen bond and slightly nonpolar because of the 2 benzene rings but I'm not sure.

Same case with Phenol.

Answer 1

Ans. Both phenol and 2-naphthol have a hydrophobic part (aromatic rings) and a hydrophilic part (hydroxyl group). Note that the –OH group is polar because of large electronegativity difference between O- and H-atoms in it.

Hydrogen bond is weak attractive forces between a highly electronegative atom (F, N, O-atom) and a H-atoms linked to such atoms. Therefore, owing to the presence of –OH group, both the molecules can form intermolecular H-bonds with water. So, both are expected to be soluble in water to some extent.

Presence of hydrophobic aromatic ring retards their solubility in water. Since the hydrophobic part of 2-naphthol (2 rings) is more bulkier than that of that of phenol (1 ring), the former molecule (2-naphthol) is much less soluble in water. Or, hydrophobic extent is exceedingly prominent in 2-naphthol, thus making it almost non-polar and insoluble (solubility less than 1.0 g / 100 mL) in water.

Summary: Both the molecules are expected to be polar because of presence of –OH group in them.

Phenol is (relatively) polar due to presence of –OH group and lower extent of hydrophobic effect from aromatic ring.

However, 2-naphthol is non-polar in spite of having a –OH group due to very prominent hydrophobic effect from bulky aromatic rings.